feat(type-provider): PHPUnits TestCase autocompletion for $this (#11)

Add basic auto completion when using `$this` inside closure in pest tests.

The autocompletion is only for phpunit testcase.

src/main/java/com/pestphp/pest/types/ThisTypeProvider.java

@@ -0,0 +1,61 @@
+package com.pestphp.pest.types;
+
+import com.intellij.openapi.project.Project;
+import com.intellij.psi.PsiElement;
+import com.intellij.psi.util.PsiTreeUtil;
+import com.jetbrains.php.lang.psi.elements.*;
+import com.jetbrains.php.lang.psi.elements.impl.FunctionReferenceImpl;
+import com.jetbrains.php.lang.psi.resolve.types.PhpType;
+import com.jetbrains.php.lang.psi.resolve.types.PhpTypeProvider4;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
+
+public class ThisTypeProvider implements PhpTypeProvider4 {
+    private final Set<String> PEST_TEST_FUNCTION_NAMES = new HashSet<>(Arrays.asList("it", "test"));
+    private final PhpType TEST_CASE_TYPE = new PhpType().add("\\PHPUnit\\Framework\\TestCase");
+
+    @Override
+    public char getKey() {
+        return '\u0221';
+    }
+
+    @Nullable
+    @Override
+    public PhpType getType(PsiElement psiElement) {
+        if (!(psiElement instanceof Variable)) return null;
+        if (!((Variable) psiElement).getName().equals("this")) return null;
+
+        Function closure = PsiTreeUtil.getParentOfType(psiElement, Function.class);
+
+        if (closure == null || !closure.isClosure()) return null;
+
+        if (!(closure.getParent() instanceof PhpExpression)) return null;
+
+        if (!(closure.getParent().getParent() instanceof ParameterList)) return null;
+
+        ParameterList parameterList = (ParameterList) closure.getParent().getParent();
+
+        if (!closure.getParent().equals(parameterList.getParameter(1))) return null;
+
+        if (!(parameterList.getParent() instanceof FunctionReferenceImpl)) return null;
+
+        if (!PEST_TEST_FUNCTION_NAMES.contains(((FunctionReferenceImpl) parameterList.getParent()).getName())) return null;
+
+        return TEST_CASE_TYPE;
+    }
+
+    @Nullable
+    @Override
+    public PhpType complete(String s, Project project) {
+        return null;
+    }
+
+    @Override
+    public Collection<? extends PhpNamedElement> getBySignature(String s, Set<String> set, int i, Project project) {
+        return null;
+    }
+}

src/main/resources/META-INF/plugin.xml

@@ -22,6 +22,8 @@
     <extensions defaultExtensionNs="com.jetbrains.php">
         <testFrameworkType implementation="com.pestphp.pest.PestFrameworkType"/>
         <composerConfigClient implementation="com.pestphp.pest.PestComposerConfig"/>
+
+        <typeProvider4 implementation="com.pestphp.pest.types.ThisTypeProvider"/>
     </extensions>
 
     <actions>